In a prior art fluid machine, for example shown in Japanese (Non-examined) Patent Publication S63-96449, heat energy is collected by Rankine cycle, wherein a compressor is also used as an expansion device for converting the collected heat energy into mechanical rotational force.
The applicant of the present invention has applied for a patent application in Japan under Japanese Patent Application No. 2003-141556, in which the scroll type fluid machine is proposed to perform compression and expansion of working fluid by rotating the fluid machine in a forward and backward direction. The fluid machine is used for an air conditioning apparatus for a motor vehicle, in which a refrigerating cycle is also used as a Rankine cycle for collecting waste heat from an engine.
The fluid machine has a pump mode function for compressing working fluid when it is driven by a driving force from an engine or an electric motor, or from both of them, and further a motor mode function for performing an expansion movement when it receives energy from the working fluid.
The compressor device of the fluid machine sucks gas-phase refrigerant into working chambers and compresses the same by decreasing the working chambers to discharge a compressed refrigerant when it receives a driving force from an outside energy source, whereas the expansion device increases the working chambers by introducing expanding the high-pressure gas in the working chamber to generate mechanical energy.
FIG. 12 is a pressure-enthalpy diagram showing a change of state of the working fluid (refrigerant) in the pump mode (compression) and motor mode (expansion) operations. As seen from FIG. 12, the change of state is different from each other due to the compression and expansion of the refrigerant. When the scroll type compression device is used as the expansion device, there is a problem in that the fluid machine can not perform the expansion operation at its maximum efficiency.
When the scroll type fluid machine is operated as the compression device, the working fluid is sucked from an outside portion of scroll wraps and compresses the working fluid. In this operation, an outside working chamber immediately starts its compression when the working chamber is closed. At the starting period of the compression, since there is a little pressure difference between the working chamber and the outside thereof, the working fluid is hardly leaked from the working chamber.
On the other hand, when the scroll type fluid machine is operated as the expansion device, the high pressure working fluid is introduced into an inside working chamber and expanded outwardly along the orbital movement of a movable scroll. When the working chamber reaches at its end stroke (comes to its outermost working chamber position), the pressure of the working fluid has still a certain high amount and therefore is likely to be leaked from the working chamber.
As above, when the scroll type fluid machine is used as the expansion device, it is important to keep a high sealing effect at outer portions of scroll wraps. It is preferable to extend, as long as possible, a seal element to be provided at a front end of the scroll wrap of a fixed scroll to increase the sealing effect. When the seal element is extended longer, then it becomes necessary to make a movable scroll larger so that an outer end portion of the seal element may not be brought out of contact from a bottom surface of the movable scroll.
This is because the outer end portion of the seal element may be damaged by the movable scroll, when the seal element becomes out of contact with the bottom surface of the moving scroll in accordance with a rotation (orbital movement) of the movable scroll and is brought into contact again with the movable scroll when it is further rotated.